The concentration of liquid products is often desired because it allows for reduced volumes to be stored and transported, thereby resulting in decreased storage and shipping costs. Liquid concentrates also permit packaging and use of the liquid products in more efficient ways. For example, with the popularity of on-demand beverage systems, which provide single servings of hot and cold beverages, concentrated forms of beverages are often utilized in a cartridge or pod to provide regular strength beverages when diluted by the beverage system. Concentration of dairy milk is such an example that is typically used with on-demand beverage systems to provide lattes, cappuccinos, and other hot and cold beverages through the dilution of the dairy milk concentrate. There are, of course, other uses for concentrated beverages.
Many consumers, however, prefer soy milk rather than dairy milk. Unfortunately, the techniques to prepare stable, highly concentrated dairy milk do not readily transfer to the formation of stable, highly concentrated soy milk. During concentration, it appears that the protein-protein interactions of the soy protein do not react the same as the protein-protein interactions of the casein and/or whey in dairy milk. Consequently, employing dairy milk concentration techniques to soy milk does not result in highly concentrated soy milks that are stable or organoleptically-pleasing.
Traditional methods of soy milk concentration, on the other hand, result in highly concentrated soy milks that are not stable and/or organoleptically-unpleasing. For example, soy milk is commonly concentrated by using an evaporator under vacuum until the desired concentrate level is achieved. However, such methods generally can not produce a soy milk concentrate that is thermal or shelf stable above about 3 to about 3.2× based on the amount of protein.
When concentrating soy milk above 3.2× based on protein using traditional evaporative methods, the resultant product has a tendency to undergo protein gelation or exhibit protein precipitation upon sterilizing (i.e., high temperature processing and the like) or during an extended shelf life. For example, when subjected to retort heat treatment conditions (i.e., about 121° C. or higher), soy milk that has been concentrated above about 3.2× based on protein using standard evaporative techniques tends to exhibit soy protein aggregation forming a network gel or a portion of the soy protein precipitates out of solution. These undesired effects upon heat treatment render it difficult to dilute the concentrated soy milk back to a single strength beverage. Additionally, consumers would find such product visually and esthetically unappealing.
Processing aids, such as sugars, are often employed with dairy concentrates to help solubilize protein and provide a stable concentration. Use of such processing aids in concentrated soy milk, however, has been met with limited success. For example, Japanese Patent No. 7-115899 utilizes sugar to stabilize soy milk and allows production of a soy concentrate having total solids of about 29.5 percent with a ratio of soy solids to sugar ranging from 1:0.5 to 1:1.5. However, due to the added sugar, the level of soy solids and protein in the concentrated soy milk is limited to less than about a 2.5× to a 2.9× concentration.
Other methods to process soy milk using heat treatments are known, but generally do not encounter the above described stability problems because these methods either do not concentrate, provide soy in a powdered form, or remove portions of the soy protein from the final product. For example, Japanese Patent Nos. 56051950 and 61040776 and U.S. Pat. No. 6,103,282 disclose methods of processing and heat treating soy milk, but do not concentrate the soy milk prior to the heat treatment. Japanese Patent Nos. 06153841, 62166859, and 06303901 and International Publication No. 98/07329 provide powdered soy milk rather than concentrated liquid soy milk. A soy beverage prepared from powdered soy milk will generally result in a less satisfactory beverage and can result in a grainy product if agglomerates are formed during reconstitution. Japanese Patent Nos. 59166048 and 62166859 disclose methods of making concentrated soy milk but do so by providing a soy milk product with decreased levels of protein.
Accordingly, there remains a need for a method of concentrating soy milk above 3.2× level to provide a product that is stable under heat treatment and has an extended shelf life. The present invention provides such needs.